This design is about 4 times more complex than a single ended input design, and not any quieter.

If taken as an isolated block. If you can be sure that there will never be common-mode noise induced at nanovolt levels between the cartridge and the preamp, including pickup of fields by the cartridge, great. Someone who is more concerned with overall system performance might prefer that common mode pickup be rejected.

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"Pity, wrath, heroism, filled them, but the power of putting two and two together was annihilated."- EM Forster

If taken as an isolated block. If you can be sure that there will never be common-mode noise induced at nanovolt levels between the cartridge and the preamp, including pickup of fields by the cartridge, great. Someone who is more concerned with overall system performance might prefer that common mode pickup be rejected.

Getting decent real world common mode rejection is very difficult. Bill Whitlock has written a lot about the problem. If there is an unbalance in impedance to ground anywhere in the chain the CMRR goes out the window. There is nothing about a transducer that makes its output intrinsically balanced unless it has a center tap. And that will only be true at DC. MC cartridges make it easier, since they are so low Z, to reject voltage fields. But they can be very sensitive to magnetic fields. Optimizing all the pieces to work well together would really require different wiring and connectors from the shell out. The ground reference for the system would be in the headshell. An avid DIYer could make this work but not without a lot of effort. I think most dealers would throw it back at a manufacturer as too much trouble.

That's actually not too far from how I (and several others) have wired our turntables- the "ground" wire connects to the phono preamp chassis and the cartridge is connected via a screened, twisted pair. As I mentioned, the CMR is good enough that I can't seem to induce hum even using extreme measures.

There's a very nice writeup about this in "Valve Amplifiers."

I disagree about the center-tap bit. That can actually degrade CMR.

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"Pity, wrath, heroism, filled them, but the power of putting two and two together was annihilated."- EM Forster

Bill Whitlock has written a lot about the problem. If there is an unbalance in impedance to ground anywhere in the chain the CMRR goes out the window.

Yes, when you're talking about typical electronically balanced inputs. Transformers are a whole other matter. A good transformer can give you good common-mode rejection even when driven from a wholly unbalanced source due to their incredibly high common-mode input impedance.

It's precisely that characteristic of transformers that Bill was looking to emulate with his inGenius circuit that he licensed to THAT Corp.